The use of wireless communication for in-home, in-building networks and point-to-point communications is increasing in popularity and spawning relatively new standards including, but not limited to Bluetooth, IEEE 802.11a, and IEEE 802.11b. As is known for wireless communications, data is modulated on to at least one radio frequency (RF) carrier frequency and transmitted as a RF modulated signal by a radio transmitter. A radio receiver receives the RF modulated signal and demodulates it to recapture the data.
As is further known, there are a variety of modulation/demodulation protocols that may be used for wireless communications. Such modulation/demodulation protocols include amplitude modulation (AM), frequency modulation (FM), amplitude shift-keying (ASK), frequency shift-keying (FSK), phase shift-keying (PSK), orthogonal frequency division multiplexing (OFDM), or variations thereof. As is also known, Bluetooth utilizes an FSK modulation/demodulation protocol, while IEEE 802.11a and IEEE 802.11b utilize OFDM and/or a form of PSK for its modulation/demodulation protocol.
Regardless of the particular modulation/demodulation protocol, a radio receiver generally includes an antenna section, a filtering section, a low noise amplifier, an intermediate frequency (IF) stage, and a demodulator. In operation, the antenna section receives RF modulated signals and provides them to the filtering section, which passes RF signals of interest to the low noise amplifier. The low noise amplifier amplifies the received RF signals of interest and provides them as amplified RF signals to the IF stage. The IF stage includes one or more local oscillators, one or more mixers, and one or more adders to step-down the frequency of the RF signals of interest to an intermediate frequency or to base-band. The IF stage provides the intermediate frequency signals or base-band signals to the demodulator, which, based on the demodulation protocol, recaptures the data.
The particular implementation of a demodulator is dependent on the demodulation protocol. For example, an FSK demodulator, which may be used in a Bluetooth compliant radio receiver, includes an analog-to-digital converter, frequency-to-signal converter (e.g., inversed fast Fourier transform), and a data recovery system. The analog-to-digital converter converts the intermediate frequency signals into a digital format. The frequency-to-signal converter converts the digital signals from the frequency domain into the time domain. For example, the frequency-to-signal converter converts a frequency encoded “0”, which may be represented by a −160 KHz frequency shift, into the time domain as a negative pulse of a known duration; and converts a frequency encoded “1”, which may be represented by a +160 KHz frequency shift, into the time domain as a positive pulse of a known duration.
The data recovery system receives the time domain pulses as an encoded signal and recaptures data therefrom. For the data recovery system to reliably recover data from the encoded signal, DC offsets that result from a fixed difference between the transmit frequency and the receive frequency need to be removed from the received encoded signal. After accounting for the DC offset, the data recovery system uses a plurality of parallel correlators or an over sampling correlator to sample the encoded signal and recover the data therefrom. While such correlators provide adequate data recovery, they are complex circuits, which consume valuable integrated real estate and add cost to the manufacturer of such integrated circuits.
Therefore, a need exists for a method and apparatus of data recovery that eliminates the need for multiple parallel correlators and also eliminates the need for an oversampling correlator and yet provides accurate data recovery.